Fine Particle Mass and Gas-Particle Partitioning of Semivolatile Organic Aerosol Emissions
from Combustion Sources
Andrew P. Grieshop, Allen L. Robinson
Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Ave.,15213, Pittsburgh, PA, USA
Diesel engines, wood stoves and other combustion systems emit large quantities of semi-volatile organic compounds
(SVOCs). The fine particle emission rate depends on the gas-to-particle partitioning of this material, which varies
with both concentration and temperature. Prior work has demonstrated that organic aerosol emissions evaporate upon
dilution due to changes in gas-particle partitioning. This paper investigates partitioning of organic emissions at nearambient conditions of diesel exhaust, lubricating oil and wood-smoke aerosol. Aerosol were diluted in two stages:
the first during injection into a dark 10 m3 Teflon-lined smog chamber, and the second when chamber contents were
diluted further via a rapid exchange of chamber air with clean external air. Particle concentration, chemical
composition and size were measured with an Aerosol Mass Spectrometer (AMS) and a Scanning Mobility Particle
Sizer (SMPS). Mass lost from the particle phase due to repartitioning (evaporation) of SVOCs was determined by
comparing the particle median diameters and dilution-corrected particle mass concentrations before and after
dilution. For example, 30% of fine particle mass in diesel engine exhaust evaporates during dilution from particle
concentrations of 400 to 70 µg m-3; another 30% of particle mass evaporates with dilution from 100 to 10 µg m-3.
Motor oil exhibits partitioning behavior similar to diesel exhaust. Evaporation of SVOCs from these sources occurs
over tens of minutes. Similar results will be presented for wood smoke. The volatility distribution of the emissions is
determined by fitting the data with absorptive partitioning theory using a basis set of saturation concentrations. The
fit for diesel emissions indicates that as little as 30% of the organic mass measured as particulate mass using quartz
filters and dilution samplers – operating at ambient temperature and high concentrations -- will remains in the
particle phase after the emissions are diluted to background organic aerosol concentrations. These findings have
important implications for the characterization and simulation of organic emissions from high temperature sources.